AVOIDING PROBLEMS WITH CARBON DIOXIDE.  
This article is intended as a follow-on from the article that appeared in Newsletter No.41, March 2001.  
Carbon dioxide can accumulate in the bottom of a terrarium.  As high levels of it are poisonous to most animals precautions must be taken to avoid problems for ground dwelling amphibians in either permanent or temporary vivaria.  The carbon dioxide must be vented out of the vivarium and this is most difficult in a tank that is only accessible from above.  It is of little use to increase the ventilation area at the top as this will not allow its escape and it will make it difficult to maintain the required high humidity.  A ventilation hole with netting near the bottom of the vivarium works in two ways.  An inflow of air will be created by a chimney effect when the lamps heat the top of the vivarium and the convection causes the to carbon dioxide exhaust.  With the lamps off the carbon dioxide will exhaust through the vent.  
A 10mm hole is sufficient for a moderate sized vivarium.  If the vivarium is fitted with sliding doors these should al-low sufficient ventilation unless they are totally insect proof or high in the vivarium.  Diamond drills are best for drilling glass without cracking.  It is essential to cool the drill and the best way is to build a Plasticine cup around the area to be drilled and filling this with water.  Drilling plastic is best done with a drill of the type that has a sharp point.  Putting the drill in the freezer and using it cold prevents the plastic melting and sticking to it.  
An aquarium can easily be converted as a temporary vivarium by standing it on its end and arranging a door and ventilation in the opening.  A piece of glass is cut to the width of the aquarium and a couple of holes are drilled in it and covered with mesh.  This is then fixed using silicone.  'H' profiles are fitted and the upper space is covered with netting.  Plastic should not be used for the door, as this will deform.  
Carbon dioxide can be a threat to frogs in small transport boxes.  The carbon dioxide in an inadequately ventilated box can reach a dangerously high level long before the oxygen levels become too low.  Air holes are really carbon dioxide vent-holes and should be placed accordingly.  Most transport cases only have holes in the lid that does not allow for the escape of the carbon dioxide.
Holes should be made from the inside so that any sharp plastic edges do not damage the delicate skin of the frogs.  Do not over-do the number or sizes of the holes.  Providing the carbon dioxide can escape, the low metabolic rate of the frogs is unlikely to exhaust the oxygen.  Too much ventilation can reduce the humidity which can harm the animal.
Thomas Falk